This paper details the creation of a massive (over 32,000 messages) artificially constructed ‘Twitter’ microblog stream for a regional emergency preparedness functional exercise. By combining microblog conversion, manual production, and a control set, we created a web-based information stream providing valid, misleading, and irrelevant information to public information officers (PIOs) representing hospitals, fire departments, the local Red Cross, and city and county government officials. Addressing the challenges in constructing this corpus constitutes an important step in providing experimental evidence that complements observational study, necessary for designing effective social media tools for the emergency response setting. Preliminary results in the context of an emergency preparedness exercise suggest how social media can participate in the work practice of a PIO concerning the assessment of the disaster and the dissemination of information within the emergency response organization and to the public.